In many technical and industrial applications it is required to dispense, for instance, an adhesive or like viscous fluid in a controlled manner so that a required quantity of the fluid is dispensed, e.g. discharged from a nozzle, within a predetermined period of time.
In some cases the amount of fluid to be dispensed is rather small, for instance one or a few drops, and the accurate dispensing of such small quantities is difficult to accomplish. One of the reasons for such difficulty is that the force needed to cause flow of the fluid and its discharge from, say, a nozzle, involves significant pressures being developed in the fluid upstream of the discharge point or nozzle so that if a flow-control valve is disposed a significant distance upstream of the discharge point, fluid flow tends to continue at the discharge point after the control valve has been closed, as a result of expansion of the fluid in the conduit between the valve and the discharge point, and, possibly, as a result of relaxation by contraction of the conduit when this is resilient. In the case of some fluids this additional flow or exudation at the discharge point may give rise to problems such as a change in the character of the fluid while exposed to the external atmosphere at the discharge point--for instance an adhesive may commence setting or curing--and this may in some cases affect the subsequent discharge of fluid, or degrade the fluid subsequently discharged.